Wireless communication systems allow users to communicate with other entities while allowing them to be geographically mobile. Also, today's wireless communication systems allow users to communicate with other entities in a variety of different communication modes. For example, some wireless communication systems allow users to communicate with each other in interconnect (cellular) mode, where the communication link is full-duplex, allowing all parties to transmit simultaneously. Other, or the same, wireless communication systems allow users to communicate with each other in dispatch mode (walkie-talkie mode), where the communication link is half-duplex, only allowing a single party to transmit at a particular time.
A typical wireless communication system providing dispatch communication services generally includes one or more dispatch call controllers, one or more voice packet duplicators, and a plurality of base stations (cell sites) all coupled together by way of a communications network. As discussed in more detail below, the dispatch call controllers generate messages for setting up dispatch communication links, controlling the channel floors of the dispatch communication links, and terminating the dispatch communication links. In addition, the dispatch call controller is also involved in managing the mobility of mobile communication units (MUs) from base station to base station. The voice packet duplicators generate voice packets for transmission via the established dispatch communication links. The base stations provide an interface between a wireless environment in which the MUs reside, and the wired environment of the communications network. The following illustrates an example of a conventional dispatch wireless communication system.
FIG. 1A illustrates a block diagram of a conventional wireless communication system 100. The wireless communication system 100 includes a plurality of dispatch call controllers 102-1 through 102-m, a frame relay/asynchronous transfer mode (ATM) communications network 104, and a plurality of base stations 106-1 through 106-n. The dispatch call controllers 102-1 through 102-m and the base stations 106-1 through 106-n communicate with each other by way of the frame relay/ATM communications network 104. The wireless communication system 100 provides dispatch communication services to a plurality of MUs, two of which are shown as MUs 108-1 and 108-2 assigned respectively to base stations 106-1 and 106-6. The following describes an exemplary process performed by a dispatch call controller in setting up a dispatch communication link, controlling the channel floor, and terminating the dispatch communication link.
In this example, the user of MU 108-1 desires to communicate with the user of MU 108-2 in dispatch communication mode. First, in response to the user of MU 108-1 initiating a dispatch call by selecting the target MU 108-2 and pressing an appropriate button, the MU 108-1 sends a page request targeting MU 108-2 to, for example, dispatch call controller 102-1 by way of base station 106-1 and the frame relay/ATM network 104. In response to receiving the page request, the dispatch call controller 102-1 sends a paging message to the MU 108-2 by way of the frame relay/ATM network 104 and base station 106-6. If MU 108-2 does not respond within a predetermined time interval (meaning that it may not be available), the dispatch call controller 102-1 sends a target unavailable message to the originator MU 108-1 by way of the frame relay/ATM network 104 and base station 106-1. If, on the other hand, the target MU 108-2 is available, it sends a page response to the dispatch call controller 102-1 by way of the base station 106-6 and frame relay/ATM network 104.
In response to receiving the page response from the target MU 108-2, the dispatch call controller 102-1 sends a target available message to the originator MU 108-1 by way of the frame relay/ATM network 104 and base station 106-1, and proceeds to establish the dispatch communication link between the originator and target MUs 108-1 and 108-2. During the dispatch communication call, the dispatch call controller 102-1 initially receives a channel floor request from the originator MU 108-1 by way of the base station 106-1 and frame relay/ATM network 104. The channel floor request informs the dispatch call controller 102-1 that MU 108-1 desires the channel floor to transmit a voice communication to the target MU 108-2. In response to the floor request, the dispatch call controller 102-1 allocates the floor to only the originator MU 108-1. If during the time that the originator MU 108-1 has the channel floor, the target MU 108-2 sends a channel floor request to the dispatch call controller 102-1 by way of the base station 106-6 and frame relay/ATM network 104, the dispatch call controller 102-1 sends a channel floor deny message to the target MU 108-2 by way of the frame relay/ATM network 104 and base station 106-6.
When the originator MU 108-1 completes sending the voice communication, it sends a channel floor open request to the dispatch call controller 102-1 by way of the base station 106-1 and frame relay/ATM network 104. In response to the channel floor open request, the dispatch call controller 102-1 makes the channel floor available until it receives another channel floor request. If no channel floor request is received within a predetermined hang time interval, the dispatch call controller 102-1 terminates the dispatch communication link, and sends appropriate messages to the originator MU 108-1 and target MU 108-2 via the frame relay/ATM network 104 and the respective base stations 106-1 and 106-6.
In addition to setting up dispatch communication links, controlling the respective channel floors, and terminating dispatch communication links, the dispatch call controllers also manages the mobility of MUs between different base stations. For example, if MU 108-1 detects that the RF environment to base station 106-2 is better than the RF environment of its assigned base station 106-1, the MU 108-1 may send a handover request to the dispatch call controller 102-1 by way of base station 106-1 and frame relay/ATM network 104. In response to the handover request, the dispatch call controller 102-1 may send a handover grant message to the MU 108-1 and base stations 106-1 and 106-2. The dispatch call controller 102-1 may also update a home location register (HLR) (not shown) and/or visitor location register (VLR) (not shown) to denote the new assigned base station 106-2 for MU 106-1.
As exemplified above, dispatch call controllers use the frame relay/ATM network 104 to communicate with base stations to establish, control, and terminate dispatch communications links, and also to manage the mobility of MUs between different base stations. As discussed in more detail below, the frame relay/ATM network 104 is configured to form a plurality of logical links connecting each of the dispatch call controllers to each of the base stations. Each of the dispatch call controllers has to manage its own set of logical links to the base stations. This is further explained below with reference to the following example.
FIG. 1B illustrates a link diagram of the prior art wireless communication system 100. As discussed above, the wireless communication system 100 includes the plurality of dispatch call controllers 102-1 through 102-m, and the plurality of base stations 106-1 through 106-n. As discussed above, the frame relay/ATM network 104 is configured to couple each of the dispatch call controllers to each of the base stations by way of individual logical links. Accordingly, dispatch call controller 102-1 is coupled to base stations 106-1 and 106-n by way of respective logical links 110-1-1 through 110-1-n of the frame relay/ATM network 104. Similarly, dispatch call controller 102-2 is coupled to base stations 106-1 and 106-n by way of respective logical links 110-2-1 through 110-2-n of the frame relay/ATM network 104. And likewise, dispatch call controller 102-m is coupled to base stations 106-1 and 106-n by way of respective logical links 110-m-1 through 110-m-n of the frame relay/ATM network 104.
In a particular wireless communication system, there may be 15 dispatch call controllers (m=15) and 3200 base stations (n=3200). In such a system, there would be 48,000 logical links connecting the dispatch call controllers to the base stations (i.e., 15 dispatch call controllers×3200 base stations). Accordingly, the dispatch call controllers have to track and manage the state of 48,000 logical links. Such tracking and management of logical links consume substantial amount of processing power of the dispatch call controllers. Additionally, when a link goes down for any reason, the dispatch call controller attempts to periodically reestablish connectivity via the link. This further results in additional consumption of processing power of the dispatch call controllers. Furthermore, the large amount of logical links makes it relatively difficult to troubleshoot problems within the frame relay/ATM network.